The invention relates to a method of producing an effect upon or influencing an emulsion formed of a printing ink and a dampening solution in a printing machine, and further to a printing machine suitable for performing the method.
Brief changes in pressure existing between rollers in a printing machine, or differences in a peripheral surface speed in a printing machine can be caused by an applicator roller rolling over a cylinder gap in a printing-form cylinder or by a ductor or vibrator roller striking another roller, or by similar abrupt or intermittent loading and unloading of an inking or dampening unit. In emulsion films on the two rollers affected by the changes, the changes result in streak-like or strip-like faults being formed in the emulsion, which are transferred from the rollers to a printing form on the printing-form cylinder, and considerably reduce the printing quality.
In order to counter this problem, consideration has heretofore been given to measures which suppress the sudden shocks and the onward transmission thereof, such as roller covers or blankets which absorb the shocks in a resilient or elastic and damping manner, and particularly stiff roll bearings. These measures have, however, not been able to reduce the emulsion strips or streaks to the extent hoped for.
The use of ultrasonic waves in printing machines is known in principle, but not with respect to the problems explained hereinabove.
For example, the published international patent document WO 91/18744 describes a method of eliminating gas bubbles in a printing ink which is used for flexographic or gravure printing, wherein ultrasonic energy is introduced into the printing ink, and foam formation is reduced in this manner. The ultrasonic energy can be supplied to the printing ink via anilox or gravure rolls, ink troughs or chambered doctor blades equipped with ultrasonic actuators.
A further example of the use of ultrasonic waves in printing machines is a method, described in the published Japanese Patent Document JP-SHO 62-134264 for supplying a printing ink to a gravure printing form, wherein, according to one of a number of embodiments, ultrasonic waves focused by a lens are aimed at the gravure printing plate. As is known, an emulsion formed of printing ink and a dampening solution is not used in gravure printing.
Yet another example of the use of ultrasonic waves in printing machines is a method described in the published Japanese Patent Document JP-HE1 3-90359 for controlling the water content of a printing ink emulsion in an inking unit. In this method, by an ultrasonic oscillator disposed in a water separation device, the printing ink emulsion is separated into printing ink, on the one hand, and into water, on the other hand. During the separation, the printing ink emulsion is not on any roller in the inking unit, but in the water separation device.
In addition, the published German Patent Document DE 198 27 295 A1 describes a metering device for a liquid medium, wherein the medium is set into vibration by a vibration element. The vibration element can be constructed as an ultrasonic transmitter acting upon the surface of a dip roller. The medium is either varnish or dampening solution but, in no case, an emulsion formed of a printing ink and a dampening solution.
The aforementioned published patent documents WO 91/18744, JP-SHO 62-134264, JP HEI 3-90359, and DE 198 27 295 A1 therefore provide no suggestion whatsoever regarding a solution for the problems outlined hereinbefore, namely, strip-type or streak-type emulsion faults and, with regard to the invention, merely represent more remote prior art.
It is accordingly an object of the invention to provide a method for producing an effect upon an emulsion in a printing machine by which the printing quality is improved, and to provide a printing machine suitable for performing the method so as to improve the printing quality.
With the foregoing and other objects in view, there is provided, in accordance with a first aspect of the invention, a method for producing an effect upon an emulsion formed of a printing ink and a dampening solution on a roller in a printing machine, which comprises introducing oscillations produced by an oscillation exciting device of the printing machine, which oscillates at a frequency corresponding to that of ultrasound, into the emulsion on the roller.
In accordance with another mode, the method of the invention includes setting the roller into oscillating by the oscillation exciting device.
In accordance with a further mode, the method of the invention includes providing the oscillations introduced into the roller with a frequency corresponding to that of ultrasound.
In accordance with an added mode, the method of the invention includes providing the oscillations of the roller as axial oscillations thereof.
In accordance with an additional mode, the method of the invention includes providing ultrasonic waves from an ultrasonic source disposed externally to the roller and functioning as the oscillation exciting device for forming the introduced oscillations, and directing the ultrasonic waves to the emulsion on the roller.
In accordance with yet another mode, the method of the invention includes aiming the ultrasonic waves at the emulsion approximately in the radial direction of the roller.
In accordance with yet a further mode, the method of the invention includes focusing the ultrasonic waves on a peripheral area of the roller.
In accordance with a second aspect of the invention, there is provided a printing machine having a roller for carrying an emulsion formed of a printing ink and a dampening solution, comprising an oscillation exciting device oscillating with a frequency corresponding to that of ultrasound, said oscillation exciting device being assigned to said roller for setting said roller oscillating.
In accordance with another feature of the printing machine according to the invention, the oscillation exciting device is disposed in the roller.
In accordance with a further feature of the printing machine according to the invention, the oscillating exciting device is of piezoelectric construction.
In accordance with an added feature of the printing machine according to the invention, the roller includes a roller shaft and a roller sleeve for carrying the emulsion, the roller sleeve being mounted on the roller shaft so as to be excited to oscillate in the longitudinal direction of the roller shaft by the oscillation exciting device.
In accordance with an additional feature of the printing machine according to the invention, the roller is an applicator roller rollable on a printing form.
In accordance with yet another feature of the printing machine according to the invention, there is provided a roller for carrying an emulsion formed of a printing ink and a dampening solution, and at least one ultrasonic source disposed adjacent to and separate from the roller, the ultrasonic source being directed toward the roller.
In accordance with yet a further feature of the printing machine according to the invention, the ultrasonic source is aimed at a peripheral surface of the roller.
In accordance with yet an added feature of the printing machine according to the invention, the ultrasonic source is aimed at a peripheral area of the roller located between two contact lines.
In accordance with yet an additional feature of the printing machine according to the invention, the ultrasonic source is of piezoelectric construction.
In accordance with a concomitant feature of the printing machine according to the invention, the roller is an applicator roller rollable on a printing form.
In the method according to the invention for producing an effect upon or influencing an emulsion formed of a printing ink and a dampening solution on a roller in a printing machine, oscillations produced by an oscillation exciting device of the printing machine, which for this purpose oscillates at a frequency corresponding to that of ultrasound, are introduced into the emulsion on the roller.
The invention is thus based on the finding that, under the assumption that the emulsion in this case is located as a thin emulsion film on a peripheral surface of the roller, emulsification can be promoted by the fact that the oscillation exciting device oscillates at the ultrasonic frequency. This finding is completely opposed to the method disclosed by the published Japanese Patent Document JP-HEI 3-90359, wherein de-emulsification is to be promoted by the ultrasound.
A printing machine according to the invention, having a roller that carries an emulsion formed of a printing ink and a dampening solution, is distinguished by the fact that the roller has an oscillation exciting device assigned thereto that sets the roller into oscillations, and oscillates at a frequency corresponding to that of ultrasound.
As a result of the oscillations of the roller, and the emulsion on the latter, the emulsification of the dampening solution with the printing ink is improved over the entire part of the peripheral surface of the roller that is covered by the emulsion. An inking unit including the roller or a plurality of such rollers excited to oscillate require, overall, fewer rollers than a conventional inking unit, in order to make the printing ink ready.
A further embodiment of the printing machine according to the invention, having a roller carrying an emulsion formed of a printing ink and a dampening solution, is distinguished by the fact that at least one ultrasonic source aimed at the roller is disposed adjacent the roller.
Due to the ultrasonic waves from the ultrasonic source, which strike the emulsion on the rotating roller, the emulsification is likewise improved. Strip-like or streak-like emulsion faults are eliminated by the ultrasonic waves, even before the emulsion faults can be transferred, in a manner similar to ghosting, from the roller to another roller or a printing form or plate.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as including a method for producing an effect upon an emulsion in a printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: